Conventionally, digital material, such as game software and music, is recorded on CD-ROMs (Read Only Memory), DVDs (Digital Video Disc), or other media. Its illegal use is prevented by, for example, encryption or copy protection. An associated method is disclosed in Japanese published unexamined patent application 2001-110137 (Tokukai 2001-110137; published on Apr. 20, 2001) disclosing discs and players capable of protection against illegal copying.
However, once a technological means is devised for decryption or copy protection overriding, such conventional illegal use prevention techniques for digital material can easily be circumvented for illegal use of the material with the technological means, which is an issue.